added a TODO, regarding the code-dupe going on in priority_task() methods

main.cpp

@@ -75,6 +75,7 @@ public:
     template <typename R> void priority_task(std::packaged_task<R()>&& ) = delete;
 
     /* adding tasks to the queue */
+    // TODO: use template-based policies to deal with priority tasks to avoid code-dupe.
     template <typename F, typename... Args>
     auto add_task(F&& f, Args&&... args) -> std::future<decltype(f(args...))>;